TAMPA, Florida (AP) - Mitt Romney oozed confidence and a defiant Newt Gingrich seemed to acknowledge his momentum had been checked, at least for now, as Florida Republicans voted Tuesday to decide who gets the state's 50 delegates, the biggest prize yet in the Republican presidential nomination contest.

Romney is heavily favored in the winner-take-all primary, the final and possibly pivotal contest in a high-stakes month in which the former Massachusetts governor has claimed one win and two second-place finishes so far. On Monday, he campaigned so optimistically that he broke into song.

Without predicting a winner or endorsing a candidate, Sen. Marco Rubio, R-Fla., told CNN on Tuesday: "The winner of Florida is in all likelihood going to be the nominee of our party."

But Gingrich would have none of that talk. Outside a polling place in Orlando Tuesday, he told reporters the race wouldn't be decided until June or July - "unless Romney drops out earlier."

In Palm Beach, Julian Stoopler, a 68-year-old investment adviser, said he's always liked Gingrich but ultimately decided to vote for former business leader Romney. "The condition of the country has deteriorated so badly that we need a CEO to turn it around," Stoopler said.

In Miami's Little Havana, car salesman Osvaldo Mitat, 69, favored Gingrich. He's impressed by the former House speaker's "commitment to the Cuban community," Mitat said, and Gingrich's marital history doesn't bother him - Mitat has been divorced four times himself.

"Romney also has a past," he said. "Everyone has a past."

For a time, Gingrich reset the GOP race with an overwhelming victory in South Carolina. But in the 10 days since, the contest has turned increasingly hostile and polls have swung in Romney's direction.

"With a turnout like this, I'm beginning to feel we might win tomorrow," an upbeat Romney told a crowd of several hundred at a stop in Dunedin on Monday.

Gingrich admitted that his momentum against Romney has slowed in Florida.

"He can bury me for a very short amount of time with four or five or six times as much money," Gingrich said in a television interview. "In the long run, the Republican Party is not going to nominate ... a liberal Republican."

The Gingrich campaign bragged that he had raised more than $5 million in January, more than half following his win in South Carolina, after raising $10 million total for the last three months of 2011.

Romney's campaign canceled a Tuesday morning rally, but scheduled a night celebration at the Tampa Convention Center. Gingrich planned a series of public appearances - including visits to two polling stations and a stop at the Polk County headquarters - before gathering with supporters for a primary night party in Orlando. The last polls close at 8 p.m.

During his final event on primary eve, at The Villages in central Florida, Romney broke into song, leading the crowd in a reverent rendition of "America the Beautiful," instead of just reciting the lyrics as he typically does.

The path to the Republican nomination - and the right to face President Barack Obama this fall - shifts to a series of lower-profile contests in February. The race for delegates is still in its early stages. A candidate needs to collect 1,144 delegates to win. Coming into Florida, Romney had 37 delegates to Gingrich's 26.

The other two candidates in the race will not be in Florida on Tuesday. Both Rick Santorum, who's won 14 delegates, and Ron Paul, with 4, have ceded Florida's primary to Romney and Gingrich in favor of smaller, less expensive contests. They will spend the day campaigning across Colorado and Nevada.

Romney and his allies have poured more than $14 million into Florida television advertising primarily to attack Gingrich, who has struggled to compete with Romney's fundraising ability, staffing and network of high-profile supporters. Gingrich and his allies spent roughly $3 million on Florida advertising.

Santorum bristled Tuesday when asked about Gingrich seeming to suggest the Pennsylvania senator should quit the race because Gingrich was the conservative most likely to defeat Romney.

"I don't think people should be telling other folks to get out of the race and get out of the way," Santorum told Fox News Channel. "You don't ask someone to quit just because you think you're the better candidate. I think I'm the better candidate."

GOP officials in Florida were anticipating a big turnout, more than 2 million voters, up from a record 1.9 million in the Republican primary in 2008. More than 605,000 Floridians had already voted as of Monday, either by visiting early voting stations or by mailing in absentee ballots, ahead of the total combined early vote in the GOP primary four years ago.